NAME

xpand, picnegate - adjust dynamic range

SYNOPSIS

fb/xpand [ -s ] [ input ] [ lo hi [ inlo inhi ] ]

fb/picnegate [ input ]

DESCRIPTION

Xpand linearly adjusts the dynamic range of the input picture (default standard input) mapping value inlo to lo, and inhi to hi. Lo and hi default to 0 and 255. If inlo and inhi are not specified, the lowest and highest pixel values in the input image are used. By default, then, xpand expands the image's dynamic range by mapping its smallest pixel value to zero and its largest value to 255. Option -s causes all channels of the input image to be considered together when computing default values for inlo and inhi, thus preserving the hue of rgb pictures. Otherwise, each channel is treated separately. Option -s has no effect if inlo and inhi are specified on the command line.

There is no requirement that lo be smaller than hi, or that inlo be smaller than inhi, nor that any of those values be in the range 0 to 255. Output values not in the range 0 to 255 are clamped. For example,

	xpand 0 255 255 0

inverts the pixel values of its input. For convenience, picnegate is a script that executes this command.

SOURCE

/sys/src/fb/xpand.c

SEE ALSO

picfile(9.6)